1. Field of Invention
The present invention relates to a transient voltage suppressor (TVS) circuit, and a diode device therefor and a manufacturing method thereof; particularly, it relates to such TVS circuit wherein a higher forward current can be sustained, and a diode device therefor and a manufacturing method thereof.
2. Description of Related Art
FIG. 1A shows a typical TVS circuit 1. The TVS circuit 1 is coupled to a protected circuit 2, for limiting amplitude of a transient voltage from an input/output (I/O) pad 3, so as to protect the protected circuit 2 from damages caused by the transient voltage (by static charges, for example). In general, the TVS circuit 1 includes a suppressor device S1 for clamping the amplitude of the transient voltage and for absorbing an excess current path. Because the suppressor device S1 needs to release a high current in a very short time, a large area PN junction is required, resulting in a very high parasitic capacitance. Therefore, during normal operation, the operation speed of the protected circuit 2 is lowered by the parasitic capacitance, and thus the application range of the protected circuit 2 is limited.
FIGS. 3A and 3B are a schematic cross-section diagram and a simulation curve showing a diode device 100 of the prior art TVS circuit 1 and its impurity concentration distribution, respectively. As shown in FIG. 3A, the prior art diode device 100 is formed in a substrate 11, and includes an N-type well 13, a field oxide region 12, isolation regions 12a, a P-type anode region 15 and an N-type cathode region 16. FIG. 3B is the simulation curve showing the impurity concentration from an upper surface of the P-type anode region 15 downward in the prior art diode device 100.
A method for increasing the operation speed of the protected circuit 2 is, as shown in FIG. 1A, providing at least one diode device D1 with a lower parasitic capacitance between the protected circuit 2 and the suppressor device S1. The PN junction of the diode device D1 and the PN junction of the suppressor device S1 are connected in reverse series, such that a current may flow through the diode device D1 in a forward direction, and the suppressor device S1 can absorb and release a high current once it occurs; i.e., by connecting a capacitor with low capacitance and a capacitor with high capacitance in series, the total capacitance is reduced to increase the operation speed of the protected circuit 2. However, though this method can suppress the problem of the high capacitance of the suppressor device S1, the diode devices D1 still need to sustain the high current induced by the transient voltage from the I/O pad 3. And if the TVS circuit 1 has a lower capacitance, the current which the TVS circuit can sustain is reduced, and thus the application range of the TVS circuit 1 is limited.
In view of above, to overcome the drawbacks in the prior art, the present invention proposes a TVS circuit, and a diode device therefor and manufacturing method thereof so that the TVS circuit may sustain a higher forward current, and the protected circuit may have a broader application range.